Optimization of Tribological Properties of 20CrMnTi Alloy with a Composite Bionic Texture and Graphene Coating for Gear Applications

Surface-dominated failures such as micropitting, scuffing, and rolling contact fatigue remain critical challenges for 20CrMnTi gear steel under high-stress and poor lubrication conditions. Inspired by the composite bionic “checkerboard + dot-matrix dimple” architecture found in natural surfaces, this study aims to develop an optimized biomimetic texture combined with a graphene solid lubricant coating to enhance the tribological performance of 20CrMnTi alloy. Laser surface texturing was employed to fabricate the bionic pattern on 20CrMnTi substrates, followed by deposition of an oxysilane-graphene coating. Reciprocating ball-on-disc tribological tests were conducted under both dry friction and oil-lubricated conditions. The results showed that under dry friction, the optimized textured and coated specimen achieved an average friction coefficient of ~0.18, representing a ~62% reduction compared to the untextured surface (~0.47). Under oil lubrication, the friction coefficient was further reduced to ~0.10–0.11, demonstrating a synergistic effect among the texture, graphene coating, and lubricant. Wear volume decreased by over 70% under dry conditions. The dominant wear mechanism shifted from severe adhesive–abrasive–oxidative wear to mild adhesive and abrasive wear. These findings suggest that the proposed composite bionic texture combined with a graphene coating offers an effective strategy for improving the tribological durability of 20CrMnTi gear.